What is purpose of fullers on blades?

[kronckew]

the ultimate 'blood grooved' 'shiv' knife: take a piece of steel tubing of appropriate length, bed or chair leg, about a foot should do. cut the tube at an acute angle from one end but not too acute such that you have a sturdy tip & leave al least 5 inches for the grip. sharpen. wrap grip in friction tape. push forcibly into a target containing fluid. possibly an unwilling 'volunteer'. see what happens.

i seem to recall peasants in 'seven samurai' making spears from bamboo like that. ruined the bandits day.

p.s. - to summerize my thoughts, metal was expensive, smithing techniques learned on bronze and copper weapons that maintained stiffness while reducing the required amt. of material for a specific length weapon by adding grooves and fullers would as a side effect produce a artistic appearance that might be carried on even into stronger materials where they technically might not be needed, tho if you are making a few hundred thousand sabres for queen and country, the material savings in steel, weight carried by the trooper and horse, extra calories to carry heavy swords, and transport of spares, etc. could be worth a few shekels.